The present invention relates to the transmission of light through optical fibers, and more particularly to an improved system for gating light propagated through a fixed length of optical fiber, used as a passive sensor, to increase its effective optical path.
Fiber optic sensors which utilize lengths of optical fiber cables to transmit light are widely employed as passive means for remotely detecting a variety of measurable physical quantities in an active medium. Many of the sensor effects and much of the accuracy provided by optical fiber cables depends on their optical path length in the active medium, and the typical method for improving accuracy is to increase the optical path length by increasing cable length. Although some sensor applications require optical fiber cable specifications of relatively low quality, many demand exacting optical standards, such as for index uniformity, birefringence, cladding and impurity concentrations, which are progressively difficult to maintain over extended cable lengths. Such high-quality lengths of optical fiber cable generally require special preparation in their fabrication so that, as a result, the cost of such cable lengths and the sensors in which they are utilized become very expensive, and in some cases, prohibitive.